1. Field of the Invention
The present invention relates to test systems, and more particularly to a device for preloading a load carrying connector that is subjected to both tension and compression forces.
2. Description of the Prior Art
In the prior art, U.S. Pat. No. 3,320,798 issued to M. M. Gram on May 23, 1967 discloses a structure for eliminating backlash in a grip used for specimen testing. In U.S. Pat. No. 3,320,798 the connecting link between the rod of an actuator and the grip is stressed by actually applying a load from the actuator through the link to increase the distance between facing shoulder surfaces on the end of the actuator rod and the end of the grip. A pair of spiral washers are then mechanically moved to increase the space between the end surfaces of this pair of washers. One of the end surfaces of the washer then contacts a surface of the grip and the other contacts the facing surface of the rod so that there is a mechanical filler between the facing surfaces of the grip and the rod.
The actuator is loaded to a tension load higher than that normally encountered during testing the specimen, so that during actual use the spiral washers remain under compression and all backlash is removed from the threaded or pinned connectors used for loading the grips.
Thus the problem of having backlash in connecting member that are loaded alternately in tension compression has long been present, and U.S. Pat. No. '798 has been effective in moving such backlash under situations where there is adequate space for the spiral washers.
Other types of tension testing machines that can utilize preloading devices or are of general interest are shown in Patents such as the following:
U.S. Pat. Nos. 3,163,036 3,421,366 3,563,086 3,800,589 4,018,080
The present device conserves space, and permits prestressing a link with a separate actuator, different from the primary testing actuator and using the stress link to eliminate backlash in the loading path.